A PCB Surface Finish for the 21st Century

多年来，基本的印刷电路板制造工艺几乎没有什么变化，仍然是一系列复杂的操作，包括成像、蚀刻、钻孔和层压，使用一系列化学品和大量水，以及产生大量污水。后面的操作之一是在组件将被焊接的铜接触区上涂上一层“表面光洁度”。这种表面光洁度可防止铜氧化，如果发生氧化，将危及印刷电路板基板和组件之间的焊点，并导致产品故障。一些用于表面处理的化学品是有毒的，比如镀金过程中使用的氰化物。几年前，人们曾试图开发一种类似的涂层，但由于几个原因，这一尝试未能在市场上获得吸引力，主要是因为含有卤化物的材料在电子行业正在逐步淘汰，而且当时人们对减少用水量等环境问题几乎没有真正的兴趣。所有行业都面临着越来越大的压力，要求它们变得对环境更负责任。因此，人们对不使用水、不产生废物的纳米涂层方法重新产生了兴趣。某类无卤化物材料已被确定为原始纳米涂层的潜在替代品，到目前为止，测试结果令人鼓舞。除了卤化物的问题外，原始涂层还存在另外两个关键技术问题，将在重新配方中解决。使用等离子涂层进行这种应用将极大地减少印刷电路板制造中的水和能源消耗，并随之减少二氧化碳排放。这项新技术可以实现显著的成本节约。在原始材料中观察到了一种不寻常的各向异性特性，即z轴电导率，其中一个轴上的每纳米电阻比其他两个轴上的低得多。这是建议的表面光洁度能够取代金属表面光洁度的关键，并且需要不受任何配方变化的影响。

The basic PCB manufacturing process has changed very little in over the years, remaining as a complex series of operations involving photo-imaging, etching, drilling and laminating, using a range of chemicals and large quantities of water as well as producing a large amount of effluent. One of the later operations is to apply a 'surface finish' to the copper contact areas where components will be soldered. This surface finish prevents oxidisation of the copper which, if it occurs, will compromise the solder joint between the PCB substrate and the components and leads to product failure. Some of the chemicals used for surface finishes are toxic such as cyanide, which is used in the gold plating process.An initial attempt was made several years ago to develop a similar coating, but this failed to gain traction in the market for several reasons, principally due to the material containing halides which were being phased out in the electronics sector and also, at the time, there was little real interest in environmental issues such as reducing water consumption.There is a growing pressure on all industries to become more environmentally responsible. Consequently, there has been a renewed interest in a nanocoating method that uses no water and produces no waste. A certain class of halide free materials has been identified as a potential alternative to the original nanocoating and test results to date have been encouraging. Apart from the issue of halides, two other key technical issues were identified with the original coating, which will be addressed in the reformulation.The use of plasma coatings for this application will dramatically reduce the water and energy consumption in PCB manufacturing along with a consequent saving in CO2 emissions. Significant cost savings can be achieved with this new technology.An unusual anisotropic property was observed in the original material, that of z-axis conductivity in which the resistance per nanometre is much lower in one axis than in the other two axes. This is key to the proposed surface finish being able to replace metallic surface finishes and needs to be unaffected by any formulation change.